This application claims the benefit of a priority under 35 USC 119 to French Patent Application No. 0015129 filed Nov. 23, 2000, the entire contents of which are incorporated by reference.
The present invention concerns medical radiology and, in particular, the galactography technique in mammography.
Mammography is an imaging technique used, notably, for the detection of breast cancers. It involves an examination which is the first among three stages of medical follow-up, namely: detection, for example, of a breast cancer; diagnosis; and intervention.
Detection covers women typically in the age bracket of 40 or 50 to 70 years old. At the examination, films are taken at two different angles: one so-called craniocaudal front view, that is, in the direction from head to toe, and a mediolateral oblique (MLO) view. In the latter case, the detector is situated under the axillary space. A film is then taken of the entire mammary gland, of the axillary space and of the whole length of the breast.
The internal structure of the breast comprises fibrous tissues and adipose tissues, which contain fat. The mammary gland has a structure which resembles a natural sponge. The mass of that sponge comprises the fibrous tissues, the fat being located inside the cells of the sponge. When a projection image is made, which is the case in radiology, it is sought to obtain an image giving the most contrast between those two types of tissue. That normal structure of the breast and possibly so-called superdensity areas, generally associated with lesions which can be either cancerous or benign, are visualized. It is therefore sought to mark those areas and to characterize them in order to determine their nature.
It is also sought to detect small calcium deposits. When they are of very small size, that is, between 100 microns and 1 millimeter, it is a question of microcalcifications. If it is felt that those calcifications might possibly be malignant, the patient passes from the detection stage to the diagnostic stage. Additional views and geometric enlargements are then made to refine the radiological analysis. Some of the characteristics (density, shape) are used in order to have greater certainty as to the malignant or benign character of the site.
These analyses can be accompanied by a clinical examination (palpation of the breast, etc.).
Upon the interventional stage, several procedures are open, particularly a needle puncture on the area which seems suspicious. This protocol is often prompted by observation of an opacity or of a microcalcification.
In some cases, a nipple discharge occurs. It is then important to study the structure behind the nipple. In addition to adipose and fibrous tissues, there is an arborescent network of ducts called galactophores, which bring the milk to the nipples. The endings of those ducts at the nipple, called galactophorous orifices, typically number fifteen to twenty. When there is a nipple discharge, the galactophorous orifice at the source thereof is marked and the duct concerned is visualized by a so-called galactography technique.
Up to now, galactography has been carried out solely with images on standard X-ray film. The technique consists of dilating the galactophorous orifice with a needle or a plastic cannula. Once the orifice is sufficiently dilated, an X-ray attenuating contrast medium is injected by that needle or cannula.
The galactophorous orifice is then closed by a wax-base plug. The breast is compressed by means of a compression plate and a radiological image is made of the entire breast. That makes it possible to see the galactophorous network which has been injected.
The examination can thus be summed up in the following stages: i) beginning with the uncompressed breast, ii) dilation of the galactophorous orifice, iii) injection of contrast medium, iv) closing of the orifice, and v) compression of the breast on the film.
By analyzing those structures, some lesions can be marked, for example, galactophorous ducts which are intersected, dilated or otherwise approached, and pathologies situated inside the galactophorous ducts can thus be detected.
With this technique, a problem arises when the breast is very dense, so that the galactophorous ducts are hardly visible, even with injection of a contrast medium.
Furthermore, when a film is used, a good contrast (that is, good information legibility) requires the density of the X-ray flux reaching the film to come within a lower limit and an upper limit. As a result, the image can be saturated if the breast is dense and, therefore, does not offer good visibility of the galactophorous ducts.
Similar difficulties are also encountered in other aspects of mammography.
In light of these problems, the invention proposes a mammography approach which takes advantage of techniques of digital processing of the radiological image in order to improve information legibility.
According to an embodiment the invention concerns a method of obtaining mammo-graphic images intended for galactography comprising the following stages:
a. acquiring a first radiological image of the breast in a compressed or immobilized state;
b. introducing a contrast medium in a part of the breast;
c. acquiring at least a second radiological image of the breast in the compressed or immobilized state and with contrast medium; and
d. partial or complete subtraction of the first image in relation to the second image, or vice versa.
It is observed that, depending on the application of the invention and, notably, the radiation energies used, just holding the breast during the procedure can actually be envisaged, without having to compress it, or compressing it only slightly.
The first and second radiological images are advantageously obtained by means of a digital X-ray detector.
The contrast medium can be introduced in at least one galactophorous duct by injection in the nipple via at least one galactophorous duct. The contrast medium is preferably introduced when the breast is in the compressed or immobilized state. In a preferred embodiment, the contrast medium is introduced by a catheter or the like, which can be maintained in an adjustable position along at least one of the following axes: a lateral axis x in the patient""s right-left direction; a lateral axis y in the costal grid-nipple direction; and an axis z in the direction of the thickness of the breast and preferably on both lateral axes x and y and axis z. The catheter or the like can be further adjustable in polar orientation. It can also be arranged to synchronize the movement of the catheter or the like along axis z, in the direction of the thickness of the breast, with the movement of compression of the breast.
The subtraction is advantageously of logarithmic type. Furthermore, a weighting factor can be applied to at least one among the first and second images and so as to obtain controlled visibility of the tissues superposed on the opacified parts. At least one of the weighting factors can be modified in real time in order to change the relative contrast of the opacified part of the breast and, notably, the galactophorous ducts and neighboring tissues.
With the method, at least one image can be acquired during introduction of the contrast medium in order to obtain information concerning the dynamics of progression of the contrast medium in the breast and, notably, in the galactophorous network.
The method can further include a stage of resetting of the first and second images before the subtraction, for example, by means of an xe2x80x9celasticxe2x80x9d resetting algorithm.
In a customary application of the invention, the radiological images are obtained with X-rays presenting a maximum number of photons with an energy around 20 keV, which favors contrast of the breast tissues. However, in order to obtain better visibility of the contrast medium, iodinated, for example, an X-ray beam can be used advantageously with a spectrum of higher energy, for example, with a maximum number of photons around 35 keV.
According to an embodiment of the invention concerns an apparatus specifically adapted for obtaining mammographic images, intended for galactography, comprising combined in one unit: means for maintaining a breast compressed or immobilized; and means for holding a catheter or the like for introducing a contrast medium in the breast.
The means for holding is arranged to permit adjustable positioning of the catheter or the like along at least one among the aforesaid three axes x, y and z and preferably the set of both lateral axes x and y and axis z. The apparatus can include means of adjustment of the catheter or the like on a polar orientation. The means for holding can include means for grasping the catheter or the like by clipping or clamping. In the preferred embodiment, the means for grasping are guided in direction z of compression of the breast in a block mounted moving on two axes x and y in a lateral plane. If need be, the means for grasping can be arranged for positioning to be adjustable by motor drive for at least one of the axes x, y and z. The apparatus can further include means for synchronization of movement of the catheter or the like in the direction of compression of the breast with the movement of compression of the breast. The means for holding a catheter or the like are advantageously configured to make possible the introduction of the latter in a galactophorous orifice of the breast before compression of the breast and to keep the catheter in that orifice during compression of the breast. A housing can be provided for a digital X-ray detector positioned directly under the breast.
According to a third embodiment of the invention concerns a mammography system intended for galactography, comprising the apparatus, the latter being set up on the axis of emission of an X-ray source, a digital X-ray detector and its means for control, and means for processing the images obtained by the latter.
The means for image processing advantageously includes means for a subtraction of images taken, on the one hand, before and, on the other, during and/or after introduction of the contrast medium. The means for image processing can further include means for image resetting used in subtraction.
An embodiment of the invention also concerns the use of the aforesaid system for digital galactography by image subtraction.